1. Field of the Invention
The present invention relates to an ink jet printer head, such as a piezoelectric-type one, and an ejector unit for use in the printer head and having a nozzle and an actuator to eject a droplet of ink from the nozzle, and particularly to such an ejector unit which has a structure assuring that the ejector unit per se can be accurately assembled and that a plurality of ejector units can be fixed to a frame member of a printer head that has an ink-supply passage to supply ink to the ejector units, while the ejector units can be accurately positioned relative to each other.
2. Discussion of Related Art
An on-demand-type piezoelectric ink jet printer head is disclosed by, e.g., Japanese Patent Application Publication No. 2002-144590A1 or its corresponding U.S. Patent Application Publication No. 2002-0024568A1. The known printer head employs an ejector unit including a cavity unit consisting of a plurality of sheet members stacked on each other. The stacked sheet members include a nozzle sheet having a number of nozzles arranged in at least one array; at least one manifold sheet stacked on the back surface of the nozzle sheet with an adhesive and having at least one ink manifold communicating with an ink supply source; a base sheet having a number of pressure chambers communicating with the nozzles, respectively; and a spacer sheet interposed between the base sheet and the manifold sheet and having first ink channels connecting between the ink manifold and the pressure chambers and second ink channels connecting between the pressure chambers and the nozzles. The ejector unit additionally includes an actuator that is bonded to the back surface of the cavity unit and is operated to apply an energy (e.g., a pressure) to each of the pressure chambers so as to eject a droplet of ink from the each pressure chamber via a corresponding one of the nozzles.
The above-identified document recites that two or more ejector units are fixed, with an adhesive, to respective recesses formed in a lower surface of a frame member formed of a synthetic resin. To this end, the above-indicated nozzle sheet of each of the ejector units has two positioning holes in two opposite end portions thereof, respectively, that are opposite to each other in the direction in which the nozzles are arranged in the array, and two or more pairs of positioning pins of a jig are fitted in the respective pairs of positioning holes of the respective nozzle sheets of the ejector units, so that the ejector units, fixed to the frame member, extend parallel to each other and are distant from each other by a predetermined distance.
Meanwhile, when the nozzle sheet having the nozzles is bonded to a channel unit consisting of stacked sheet members having the pressure chambers and the ink channels, the above-indicated two positioning holes of the nozzle sheet have conventionally been used to accurately position the ink channels and the nozzles relative to each other,
That is, the two positioning holes of the nozzle sheet are used twice in two operations, i.e., the first operation to prepare the ejector unit by bonding the channel unit and the nozzle sheet to each other, and the second operation to attach the ejector unit to the frame member. In the first operation, however, when positioning pins of a first jig are fitted in the positioning holes of the nozzle sheet, or are pulled out of the positioning holes, the positioning holes may be deformed and/or the diameter thereof may be increased. In this case, in the second operation in which the positioning holes are used for the second time, positioning pins of a second jig may not be fitted in the positioning holes, or may rattle in the positioning holes. In addition, in the case where two or more ejector units are fixed by adhesion to the frame member, it is difficult to accurately align the direction of extension of each of the nozzles of the ejector units with respect to a reference direction on the frame member. Moreover, the degree of parallelism between the respective nozzle arrays of the ejector units, and/or a distance between the respective nozzle arrays may suffer an increased error, so that ink is recorded, on a recording medium such as a sheet of paper, at a position deviated from a correct position. This means a lowered accuracy of printing of the printer head,